It is the special move in the red stance. Your Jedi jumps toward the opponent and does an overhead strike that buries the saber into the ground. It was an unblockable one hit kill move and to top it off you could swing your self around mid jump and once you land so people would abuse it by jumping into crowds of people with DFA and doing a 360 killing everyone.

You used to execute it by pushing the attack button then pushing forward and jump in unison once both hands hit the saber (although you could delay it to half way through your attack). But now you have to keep the attack button held down as you push forward and jump. The timing is identical.

The damage has been reduced and you can no longer turn while doing it. It is basicly a worthless move now. Unless you are in a corridor or your opponent is cornered.